1. Field of the Invention
The present invention relates to a window device for use in a motor vehicle, in particular, to a window device for use as a sunroof in a motor vehicle.
2. Description of the Related Art
For a long time, it has been known that a window device for use as a sunroof in a motor vehicle is made of a polymethyl methacrylate resin or a polycarbonate resin, since this kind of material has only a very small specific gravity and thus it is considered suitable for use as an appropriate material of a light transmissible member for manufacturing a light weight motor vehicle. In a case where a window of a motor vehicle is made of a synthetic resin, since a synthetic resin has a lower elastic modulus than a glass material, the resin material is usually combined with an iron or aluminum reinforcing material along the edge portions of the window so as to obtain a desired reinforcement to prevent a possible bending or twisting.
However, there has been a problem with a window made of a synthetic resin. That is, a resin window panel has a comparatively large deformation amount caused by a thermal expansion due to a temperature change. In fact, such kind of thermal deformation amount is larger than an iron or aluminum material which is usually employed to make a reinforcing member in a window. To cope with the above problem, it has been suggested that a resin window panel be laterally movably combined with reinforcing members which are to be secured on the vehicle main body, so as to form a thermal expansion absorbing structure which is cable of absorbing a thermal expansion caused by a temperature change. This kind of thermal expansion absorbing structure may, for example, be found in Japanese Unexamined Patent Publication No. 62-214011.
FIG. 18 is a cross sectional view indicating the above mentioned thermal expansion absorbing structure disclosed in Japanese Unexamined Patent Publication No. 62-214011. As shown in FIG. 18, tip portions 103 of a plurality of projections 102 located close to the outer edge of a resin window panel 101, are inserted in holes 105 formed through a reinforcing plate member 104, by making use of an elastic deflectable property of the resin material. Further, a sponge rubber 106, which is capable of absorbing a length change caused due to a thermal expansion of the resin window, is interposed into an annular space formed between the outer periphery of each projection 102 and the inner wall of a hole 105.
However, if a sunroof of a motor vehicle is made of a synthetic resin, and if the motor vehicle is running at a high speed, there will be a relatively large detaching force which acts on the resin window panel, resulting in a tendency to cause the resin window panel to leave its original position. In order to avoid such trouble, a combining strength of the resin window panel which is useful in combining itself with a reinforcing member, is required to be large enough to act against the above detaching force.
Nevertheless, a problem with the thermal expansion absorbing structure disclosed in Japanese Unexamined Patent Publication No. 62-214011 may be concluded as follows. Namely, since the tip portions 103 of the projections 102 of a resin window panel 101 are inserted in the holes 105 of a reinforcing plate member 104 by making use of an elastic deflectable property of the resin material, a comparatively large inserting force is needed to effect such an insertion if an engaging amount for the combination of the two (the projection 102 and the hole 105) is large. Moreover, if a large force is used to act as an inserting force, there will occur a crack or breaking in the tip portions 103 of the projections 102.